1. Field of the Invention
The present invention relates to optical nodes and, more particularly, to an integrated optical node that includes a unit for selecting a signal light of an arbitrary wavelength and at least one of a unit for transmitting a signal light and a unit for receiving a signal light of a selected wavelength, and to an optical communication network using such an optical node.
2. Related Background Art
In an optical communication network having a system of a demand-assignment type wavelength division multiplexing access (DA-WDMA) using multiplexed wavelengths, the network generally requires transmitting or receiving a wavelength (the term "wavelength" herein also refers to an optical signal having such a wavelength) carrying an access-control signal and a wavelength carrying a data signal simultaneously. Further, it is necessary to select an arbitrary wavelength for transmission and reception of wavelength division multiplexed data signals. However, to ensure that optical nodes in the optical communication network have such functions, it is necessary to arrange several separate devices in the optical node.
An example of such a prior art node will be described hereinafter. Referring now to FIGS. 1A and 1B which schematically depict one known example of prior art optical nodes described in "SB-6-6 distributed in Vernal National Conference of Japanese Academy of Electronics Information Communications, 1991", the optical node comprises the following discrete devices: a device 80a for separating a wavelength .lambda..sub.A carrying an access-control signal from an input light composed of wavelengths .lambda..sub.A and .lambda..sub.2 -.lambda..sub.N, a device 80b for coupling or multiplexing the wavelength .lambda..sub.A with wavelengths .lambda..sub.1 -.lambda..sub.N-1 of an output light, and a switching device 81 which couples a wavelength .lambda..sub.1 with the separated wavelengths .lambda..sub.2 -.lambda..sub.N and selects an arbitrary wavelength .lambda..sub.N from among the wavelengths .lambda..sub.1 -.lambda..sub.N-1. As shown in FIG. 1B, the switching device 81 includes an optical coupler or multiplexer 86 and an acousto-optic filter (A0 filter) 87 which has no polarization dependency.
For the reason set forth above, following problems have arisen with the prior art optical node:
(a). expansion of optical node size,
(b). optical loss at optical coupling elements, and
(c). optical arrangement complexity.
Moreover, these problems have become more serious since the optical node requires additional discrete devices such as electro-optical converters (E/O) 82a and 82b for converting an electric signal to an optical signal, opto-electric converters (O/E) 83a and 83b for converting an optical signal to an electric signal. Integrated into the optical node are a data register 84 which stores input and output data and an access processing circuit 85 for processing an access-control. These elements are also needed in different types of optical nodes.